Low voltage DC from the AC mains.

Fabricators of line-powered equipment who need a small amount of low voltage DC to power a microprocessor or other circuitry usually have a choice of an over-sized and expensive transformer or a high power dropping resistor. The associated PDF file presents a new low-power technique which can provide low voltage at tens of milliamperes with very low dissipation.

An important note: The circuit does not provide galvanic isolation from the AC power line and is thus dangerous to work with. YOU HAVE BEEN WARNED!

The commented schematic is available for downloading by FTP here. Circuit schematic . It's 19 kilobytes of PDF.

If you find the circuit useful I would like to know what you did with it. I used it in a microprocessor controlled hot water heater and I once thought of marketing it - a bad idea for this non-businessman.

I also have some ideas which use power MOSFETS for the same purpose. Well. . . It's now a decade later and those MOSFETs are really a better way to go because they can be turned off as well as on. I shall get around to publishing a circuit using one of those right soon now.

Doug McNutt
The MacNauchtan Laboratory
7255 Suntide Place
Colorado Springs, CO, 80919-1060
719 593 8192